Torsion balance



H. RAINBOW Tons'IoN BALANCE Filed Sept. 8. 1934 May 11, 1937."

fiel' Patented May 11, 1937 ,UNIT-ED STATES PATENT OFFICE TOBSION BALANCE Henry Rainbow, The Hag-ue, Netherlands, assignor to Naamlooze Vennootschap De Bataafsche l Petroleum Maatschappij, The Hague,

Netherlands, a Dutch company Application September 8,1934, Serial No. 743,203 v ln the Netherlands September 13, 1933 s Claims. (c1. 26S-1.5)

is placed in a nonuniform gravity ield it is s'ub-l ject to a force couple which tends to rotate the beam about the axis of the suspending thread, a counteracting couple being thereby elicited -in this thread by torsion.

The angle of rotation of the beam under the iniiuence of thetwo couples then supplies a measure for the variation of the field of gravity.l

A requirement of paramount importance in such a balance is that oi sensitiveness. A certain variation of the field ci." gravity has to cause a sumciently large, measurable deflection of the beam. Moreover, it is of great practical importance that the period of oscillation of the system be not too lons. in order that -only the shortest possible time will be required for a single observation. The said period can be reduced by shortening the horizontal distance between the weights, which however, entails a decreased sensitiveness. In itselfthis is not a very great drawback, as it can be overcome by a' refinement of the device for measuring the deilection of the beam. However, the shortening of the horizontal distance between i the weights also has the result that the disturbances due to micro-seismic vibrations of the earth i. e.'the extremely small transversal vibrations resulting from various causes begin to exert their innuenceand owing to the unequal level of the pendulum weights impart to the beam a rotatory movement to the extent of making it.`

impossible to resister thefdefie'ction.

'I'he object of the invention is to devise a beam with a short `period of oscillation and a smalli horizontal distance between the weights which nevertheless allows an accurate registrationy oi the deflection to be made. This object isattained by the-application-of measures for eliminating from the registration the action of secondary 4,5 oscillatory movements caused by micro-seismic' n sensitive to the said vibrations. A' reduction of other.

taining the beam (l) the horizontal distance between the weights makes it possible to place the pendulum in a housing of simple shape e. g. cylindrical, whereby the disturbing action on the pendulum of currents of air'within the pendulumhousing. is largely avoided.

The invention is illustrated in the accompanying drawings of which,

Fig. I- is a vertical cross section of a balance.

Fig. II is a diagrammatic view of the registering Fig. III is a vertical section 'of lower portion kof a balance showing an alternate method of suspending the beam.

Fig. IV is a side view of upper part of the beam showing an alternate method oi attaching Weights to the beam.

Fig. V is a. vertical section of a balance sus-v pended in a dampenng liquid.

Referring to Figure I2 the beam (i) consists of a tubular part carrying platforms (2B) on the upper and lower parts on which the weights (2) and (2') are placed diametrically opposite each The beam is suspended by a torsion thread '(3) which at the klower end is attached to the beam by a clamp (4) and at the top is clamped by a head (5). This head is ilxed to the upper part of the cylindrical housing (8) con- The diameter of the cylinder (6) forming part' of the beam is such as to leave a narrow space between the cylinder (8) and the wall ofthe housing (8) whereby'a dampening action -is exerted on the oscillations of the pendulum by reason of the air cushion between the cylinder and the housing (8)'.

A flat plate (1) at the bottom of the pendulum serves as-a further dampening agent by reason of the air cushion between the plate and the plug (l). In Figure I the plate (1) extends at right angles to the vertical section shown andts in a cross slit in plug (9) closing the housing (8) at the bottom. The housing (8) is integral with table (I5), cylinder (IE) and housing (I1).l The housing (I 1) contains the device for the optical determination of the position of .the beam with regard to the housing (Il). This device comilected ray is shown in two positions` The ther- .mocouple (22) 'is of a type having two Junctions i. e. two endv strips of the same metal are separated by a middle strip of a dissimilar metal. In practice I have found that a thermocouple of the type described in Zeitschrift des Vereins deutscher Ingenieure voi. 77, page 129.0, has proven very satisfactory.

The heat evolved by the reiected ray generates an electric current in the thermocouple, the in.

' tensity of which depends upon the point of impact of the ray, so that the deection oi' the galvanometer indicates the deilection of the pendulum. It is of essential importance that the inertia oi' the registration device prevent the registration by the galvanometer o! the movements of very short period about a median position resulting from the micro-seismic vibrations of the earth so that the galvanometer'only registers the median position itself. 'I'he necessary amount of inertia is particularly present in a galvanometer with a long period of oscillation of its own. The thermocouple also has a favorable influence in this respect. The housing (Il) is carried by the underframe (I3) of which the base (Il) can be put in the desired position by means of adjusting screws (l2). The housing isarranged so that it can be rotated with respect to the base (Il) and under frame (Il) by means of ball support (I0) and ball bearing (I4). servations on the same location to bemade with an altered position of the beam.

In order to eliminate the oscillations due to .35 the micro-seismic vibrations of the earth the following additional measures may be taken either separately or together.

. The lpendulum may be immersed in .a'liquid vas shown` for example at (21) in FiguteV."'lhe dampening action thus obtained 'will counteract transversal and consequently rotational oscillations. Besides providing 'a torsion'threadat ther top o! the beam, a torsion thread. may be provided plugica) of modiiiedshape. IEinallfthqeI upper weight (2) `canbe attached to the pendulum byA f means oi `an elasticmember allowing this weight `:'10 to move in a plane atright angles to that vthrough g the two-weights. This may be eilected for example as shown'in Figure I Vin whiclrthe weight (2) i. 1s attached to the beam (n byy means of les:

' cylindrical housing, av beam within said housing,

spring (28). Dynamically the attachment oi' this weight may, by a correct choice ofzthe elastic member approach the result obtained by suspen- 1. A .torsion balance comprising a balanceA beam. a torsion suspension for said beam, a couple o! weights carried by said beam, a substantially This enables further ob- Y As 'a conf I Y cylindrical housing for said beam. and a cylindrical member carried by said beam. the relation v I between the outer' diameter of the said member and the inner diameter of said housing being such that' the cylindrical member is adapted to move with little playin the cylindrical housing.

2. A torsion balance according-to claim 1 in which the beam carries a vertical, diametrically directed plate, the housing being provided with a correspondingly shaped space, in which the plate is adapted to move with little play.

3. A torsion balance comprising a beam, a torand a torsion thread bymeans of which the beam is suspended, the said beam consisting in a central tubular part, the axis of which coincides with the axis of the torsion thread, a'disc-like platform carried at each'end of the tubular part, and a weight fixed to each platform in such a manner that the weights are positioned at opposite sides of the tubular part.

5. A torsion balance according to claim 4, in which a hollowcylinder is ilxed to the beam coaxially with the tubular part thereof, the outer diameter of said cylinder being slightly smaller y.

than the inner diameter ofy the housing of th balance.

6. A torsion balance according. to claim 4, in which the lower platform of the beam carries a downwardly directed vertical plate comprising the axis of the tubular partr ofthe beam, and in which the housing has at its lower end an internal cavity, the walls 'of which surroundl the said plate with a relatively small clearance.

'1.v A torsion balance comprising a balance beam, a torsionsuspension i'or said beam, two weights carried' by `said beam, a` substantially cy- Vlindricalhousing'for'.said beam, a cylindrical member carried by saidbeam; the relation between theouter 'diameter-.of the saidniember and the inner diameter4 of 'saidhousing being `such that the cylindrical member is adapted to.

move with little play in the cylindrical housing and vdampening liquid illlingthe space between said housing and'said cylindrical member.

. 8. A torsion balance comprising a substantially a torsion thread by means of which the beam is suspended.` said beam consisting of a central tubular part, the axis of which coincides with the axis of said torsion balance, a platform at each end oi Y said'tubular part, a weight attached to each platformin such manner that the said weights are positioned on opposite sides of the tubular part.. g

and. a dampening liquid in said housing completely immersing said beam. 

